Fluid leak detection of cooling fluid in the metallurgical industry has been attempted using various techniques. One technique involves using a pair of accurate magnetic flow meters installed on the inlet and outlet of the most critical cooling circuits. This technique not only represents significant capital expense, limiting its installation to the most sensitive cooling circuits rather than a furnace wide system, it also requires regular calibration to ensure that the instrument pair reports flow discrepancies accurately.
The coriolis flow meter is one of the most accurate flow meters in industrial use today and is also one of the few flow meters that measure mass flow directly, without requiring a density correction. Furthermore, the signal is directly proportional to the flow rate, unlike many alternative measurement techniques, such as those employing an orifice plate.
When installed in its traditional configuration, the coriolis meter is capable of continuously and directly measuring the mass flow of liquid or gas through a pipe. In its most basic configuration, the flow meter consists of a u-tube through which the process fluid flows. When the tube is oscillated at a known frequency, driven by a piezoelectric or electromagnetic device, the motion of the moving fluid inside imparts an angular deflection, or twisting, of the u-tube outside of its normal geometrical plane. The coriolis force which causes the twist is directly proportional to the mass flow through the tube and hence measurement of the amount of twist allows direct determination of the mass flow rate by the instrument. Furthermore, the frequency of the tube deflection allows accurate calculation of the fluid density.
To increase the accuracy of the flow measurement, the typical industrial configuration uses a pair of parallel u-tubes, which are again oscillated at a known frequency. The process fluid flows through both tubes in the same direction and the coriolis force again causes the tubes to measurably twist; the instrument measures the angle of twist between the two sensor tubes as a phase difference between the output signals of the two electromagnetic pickups. The parallel pair tube design automatically eliminates some common-mode error sources compared to the previously discussed single tube design.
In using two separate flow meters to compare differences in flow between the supply and return conduits for the purposes of leak detection, perfect calibration of the two flow meters is required. Spurious detection of differences in flow may be caused by loss of calibration of one or both of the flow meters. Further, errors or loss of accuracy may be introduced by digitizing, comparison and calibration of the sensed measurements of each of the two flow meters.
The described embodiments attempt to address or ameliorate one or more disadvantages or shortcomings associated with existing techniques for fluid leak detection, or to at least provide a useful alternative thereto.